The present invention relates to an apparatus for controlling a plant with desirable accuracy by using a delta-sigma (ΔΣ) modulation algorithm.
As shown in Japanese Patent Unexamined Application Publication No. 20003-195908, a scheme of controlling a plant by using a delta-sigma modulation algorithm (or a sigma-delta modulation algorithm or a delta modulation algorithm) is known. As long as the plant is capable of generating an appropriate control output in response to a control input switched between “on” and “off”, the plant can be controlled with desirable accuracy by using the delta-sigma modulation algorithm.
FIG. 18 shows a block diagram of a typical controller in which a delta-sigma modulation algorithm is used. A plant 101, which is a controlled object, is modeled by using model parameters. An identifier 102 recursively identifies the model parameters based on a control input and a control output of the controlled object 101. A state predictor 103 takes into account a dead time included in the controlled object 101 to generate a predicted value for the control output by using the model parameters. The predicted value is compared with a desired value. An amplifier 104 amplifies an error between the predicted value and the desired value to output a reference input. A controller 105 applies the delta-sigma modulation algorithm to the reference input to calculate a control input to be input to the controlled object 101.
The state predictor generates the predicted value for the control output of the controlled object so as to compensate for the dead time included in the controlled object. When the controlled object has no dead time, the state predictor is not required. If the state predictor does not exist, the model parameters identified by the identifier are not reflected in the control input. As a result, the control accuracy may deteriorate.
Therefore, there exists a need for a control apparatus capable of controlling a controlled object having no dead time with desirable accuracy by using a delta-sigma modulation algorithm.
Output signal from the controller that uses the delta-sigma modulation algorithm is a square wave. When the model parameters are identified by using such a square wave signal, the model parameters may tend to vibrate. Such vibration of the model parameters may cause instability in the control system.
Therefore, there also exists a need for a controller of preventing model parameters from vibrating in the control using a delta-sigma modulation algorithm.